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Irradiance Measurements

Spectral Irradiance measurements can be done in different setups and wavelength ranges, like with fiber optic cosine corrector or integrating sphere. Irradiance measurements can be done in the UV/VIS as well in the VIS/NIR range.

For absolute irradiance measurements a spectrometer can be configured and radiometrically calibrated in Melles Griot calibration laboratory with a range from 200 to 400 nm or from 350-1100 nm or for a combined UV/VIS range of 200-1100 nm. This calibration is done on a fixed setup, i.e. fiber optics and diffuser can not be changed afterwards.

In order to be more flexible in the setup a calibration can be performed on location with 13 HLS 105 calibrated VIS/NIR light source or 13 HLS 205 calibrated UV/VIS/NIR light source.

The comprehensive 13 FSS 103 irradiance application add-on software allows you to perform and load irradiance calibrations.

A typical setup for irradiance measurement is given below.

Components used in the irradiance measurement setup:

	UV/VIS Irradiance	VIS/NIR Irradiance
Spectrometer	13 FOS 200-109 (200-400 nm), 13 FOS 202 UV detector coating, 50 µm slit 13 FOS 003	13 FOS 200-104 (360-1100 nm), 50 µm slit 13 FOS 003, 13 FOS 012 Order sorting coating
	13 FOS 200-105 (200-1100 nm), 13 FOS 202 UV detector coating, 50 µm slit 13 FOS 003 13 FOS 012 Order sorting coating
Software	13 FSS 101 Full version Software and 13 FSS 103 irradiance add-on software
Calibration	Irradiance Calibration Service, UV (200-400 nm)	Irradiance Calibration Service, Visible (360-1100 nm)
	Irradiance Calibration Service, UV to Visible (200-1100nm)
Light source (optional)	13 HLS 205 Calibrated Deuterium-Halogen light source	13 HLS 105 Calibrated halogen light source
Fiber-optics	13 FOA 102 fiber 200 µm UV/VIS, 2 m, SMA
Accessories	13 FOA 104 cosine corrector or 13 SIP 102 integrating sphere

Irradiance Application Add-on Software (13 FSS 103):

Radiated optical energy, as measured by Melles Griot spectrometers, can be quantified as a radiant flux, a measure in energy per second (Watts) radiated from a source. The radiated optical energy can be correlated with human vision (photometry) as defined in the CIE to obtain a spectral luminous efficiency function to characterize the vision of an average human observer.

Both radiometric and photometric quantities can be measured with an irradiance calibrated Melles Griot spectrometer system. Radiometric quantities are radiant energy (in Joule), Radiant power or flux (in Watt) or irradiance (Watt per cm²). Related photometric quantities are luminous flux (lumen) or illuminance (lux or lumen per m²).

With the Irradiance Application add-on software (13 FSS 103) it is possible to calculate the above parameters from the measured spectral distribution. A calibrated light source 13 HLS 105 or 13 HLS 205 with known energy output (in µWatt/cm²/nm) is used as a reference. This calibration can be performed, saved and loaded by the end user.

Another option is to have your spectrometer system calibrated in our irradiance calibration lab, so there is no need to have an additional calibrated light source. The calibration can be loaded into irradiance add-on software 13 FSS 103.

Color of light parameters can be expressed by the chromaticity coordinated x, y and z. These chromaticity coordinates are obtained by taking the ratios of the tristimulus values (X, Y and Z) to their sum. The tristimulus values Time Measurement mode, up to 8 functions can be displayed simultaneously against time. For each function, a different radiometric, photometric, photon or color coordinate output parameter and/or wavelength range may be selected, as well as a different spectrometer channels X, Y and Z and the spectral irradiance are computed in a wavelength range from 380 nm to 780 nm, using a 1 nm interval. These parameters, as well as u and v coordinates, and the color temperature of an external light source can be calculated and displayed in real-time.

The same experimental set up (spectrometer with fiber optics and cosine corrector or integrated sphere) is used to calculate the intensity of the light to be measured.

The calculated output can be displayed and saved in two ways:

1. In the Irradiance Chart the data can be displayed as spectral irradiance in µWatt/nm versus wavelength, like in the screen dump above. Further, the following output parameters can be displayed: radiometric quantities µWatt/cm², µJoule/cm², µWatt or µJoule, photometric quantities Lux or Lumen, color coordinates X, Y, Z, x, y, z, u, v and color temperature, and number of photons µMol/s/m², µMol/m², µMol/s and µMol. In addition raw data in Scope mode is displayed as well as the X-Y Chromaticity diagram, including parameters, especially useful for LED measurements, such as: Dominant Wavelength, Purity, Central Wavelength, Peak Wavelength, Centroid, etc.
2. In Time Measurement mode, up to 8 functions can be displayed simultaneously against time. For each function, a different radiometric, photometric, photon or color coordinate output parameter and/or wavelength range may be selected, as well as a different spectrometer channel.